I. Field of the Invention
The present invention relates to a circuit for controlling the current delivered through a magnetic coil of an electromagnet used in a magnetic resonance imaging device.
II. Background Information
Magnetic resonance imaging devices are known which employ large electromagnets. These electromagnets typically comprise resistive coils that are configured in a Helmholtz coil approximation. In order to generate the requisite magnetic field along the axis of such coils, a constant current of approximately 200 amperes is typically required to be delivered into the coils.
A major problem in stabilizing the current delivered to such prior art devices centers around the necessity of measuring this current accurately. A typical method of measuring such current is to pass the current through a sense resistor. The voltage developed across this sense resistor is then compared with a standard voltage and an error signal is used to control the level of current supplied. A problem with this method is that the power dissipated in the sense resistor at high current levels heats the resistor and causes changes in the resistance as well as thermoelectric voltage errors in the resultant output voltage.
It is, accordingly, an object of the present invention to provide a circuit for stabilizing electromagnet coil current of magnetic resonance imaging devices.
More specifically, an object of the present invention is to provide a circuit for stabilizing the electromagnet coil current of a magnetic resonance imaging device which has improved insensitivity to resistance and thermoelectric voltage errors.
A still further object of the present invention is to provide a circuit for stabilizing the electromagnet coil current of a magnetic resonance imaging device which provides a stabilization better than one part per million.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.